Starter Fertilizers in Corn​​​

Key Points

  • Starter fertilizer is a small amount of fertilizer placed close to the seed at planting to help enhance seedling growth and development.

  • Uniform crop establishment and early vigor are important during early growth stages and can potentially impact plant development and yield.

  • When choosing a starter fertilizer system, consider the nutrients available/supplied by the material used, application rate, and placement options available.

What is starter fertilizer?

A relatively small amount of fertilizer placed in close proximity to seed at or around planting to help enhance the growth and development of emerging seedlings is considered starter fertilizer. It is used to provide easily accessible nutrients to developing plants until they establish larger root systems. Starter fertilizer must be placed in such a manner as to enhance early seedling vigor and development, usually directly below or to the side of the seed. Starter fertilizer is usually composed of nitrogen (N) and phosphorus (P). The N in starter fertilizer can help prevent early N deficiency since cold soil conditions can slow the release of nitrogen from organic matter and P is important for promoting vigorous root growth needed for healthy, dark green plants.

Why use starter fertilizer?

Corn plant roots develop in two distinct phases, seminal and nodal roots. Seminal roots gather moisture from the soil while young seedlings use up the food reserves from the kernel. Once plants emerge from the soil, the nodal root system begins to develop which will become the primary route for water and nutrient uptake. During corn growth stages V1 through V5, it is important to prevent stress to the developing nodal root system as slowing of growth during nodal root system development can stunt the entire plant’s development and thus reduce yield potential. Around stage V3, corn plants transition from dependence on kernel reserves to nutrient uptake via nodal roots (Figure 1). The success of this transition can be the key to a healthy, uniform crop. This is where starter fertilizer comes into play.

Figure 1. Corn plant at growth stage V3, the period of transition from kernel reserves to uptake via nodal roots. Starter fertilizer can help ensure the success of this transition.

Starter fertilizer acts to provide nutrients in close proximity to immature root systems that do not yet have the size and bulk density to access necessary nutrients from the soil, especially under less than ideal soil conditions. Specific planting circumstances that may benefit from the use of starter fertilizer include: soils that have tested low in P, cool soil temperatures associated with early planting, high residue cover associated with conservation tillage situations, Northern Corn Belt locations, coarse-textured (sandy) soils low in organic matter, poorly-drained soils, soils either high or low in pH, and locations prone to substantial drought stress.

Uniform crop establishment and early seedling vigor are ideal and important during early growth stages and can potentially impact plant development and yield later in the season. Not only are healthy, fast-growing seedlings better able to compete with weeds, but they can also be more resistant to insects and diseases. Early rapid growth also helps to hasten the onset of large leaf formation which is necessary for photosynthesis.

Considerations for using starter fertilizer.

When choosing a starter fertilizer system that works best for your specific field or operation, there are three main things to consider: the nutrients available/supplied by the material used, application rate, and placement options available.

Materials. When using a starter fertilizer that contains both N and P, optimum results can be obtained when combining phosphate with ammonium nitrogen. Monoammonium phosphate (MAP; 11-52-0) or ammonium polyphosphate (10-34-0) liquid-based fertilizers are excellent choices. Nitrogen in ammonium form can help to enhance the use of P in the starter as well as P uptake from soil. Generally, starters should contain a high phosphate (P2O5) ratio and the phosphate should be highly water soluble. A fertilizer does not have to be labeled “starter” to be used as such if it meets the needs for your situation and follows basic defined parameters of rate and placement. Depending on soil test results, micronutrients can also be provided in the formulation to meet specific needs. Starter fertilizers can be applied in both solid and liquid forms as generally there is no difference in effectiveness. Liquid fertilizers may be more expensive than dry formulations, but when properly applied can require lower quantities and still be cost effective.

When a field has tested high in P, such as those on farms where manure is applied, there are a few options to gain effective starter response from fertilizer without adding significant amounts of P. One option is the use of N only fertilizers such as ammonium sulfate (21-0-0-24S) or ammonium nitrate (34-0-0). Using an N only starter may provide an adequate response, but since P is immobile in the soil, sometimes additional P may still need to be added in very close proximity to the seed for an ideal response. This may be accomplished by the use of a very low rate of starter placed with the seed as a pop-up fertilizer. This allows the developing seedling access to P without adding much to the soil profile.

Rates. Generally, only a small amount of fertilizer will be required for a starter response if soil fertility tests are within the optimum range or higher. The appropriate rate of starter to use will depend on: proximity to the seed, salt content or index, and soil texture. Using rates above the recommended limit can cause a salt effect that can impede germination and early plant development. If starter fertilizer is placed 2 inches from the seed, do not apply more than 70 lbs N plus K2O per acre and reduce even further if placed in closer proximity to seed. If starter is placed with the seed (a pop-up fertilizer) the limit should be 10 lbs/acre. Salt index is estimated to be the sum of N + K + 0.5 x S. These values are provided in Table 1. Problems associated with salt damage may develop if soil moisture is limited within the first few weeks after planting or if fertilizer was placed too close to the seed. Soil texture also plays a role in that fertilizer rates must be lowered when placed within 1-2 inches on sandy soils. For example, the amount of 10-34-10 that can be safely applied per acre on sandy soils is 20 gallons per acre, while on non-sandy soils, the amount increases to 40 gallons per acre. For narrower row-widths, the application rate may be increased. It is especially important to follow rate limits in conservation tillage due to the less accurate placement of starter in relation to the seed.

Placement. While N is mobile in the soil, P is bound and does not readily move through the soil. Starter fertilizer allows close placement of P in order for the developing plants to take it in. Placement is crucial because seedling plants must be close enough to access nutrients, but not too close when used at higher rates. The ideal placement for starter fertilizer is in a band 2 inches to the side of and 2 inches below the seed (2x2). This allows the roots easy access to the fertilizer, but limits the potential for fertilizer burn. The 2x2 placement has an advantage over seed-placed starter because it is in a prime location for nodal root development and higher rates can be used without risk to the seed.

Alternatives to the 2x2 band include: placement at 2 inches beside and at the same depth as seed; dribbling fertilizer over the seed row in front of the no-till coulter; and pop-up placement. “Pop-up” fertilizer which is placed directly in contact with the seed is an option, but requires extreme caution to avoid seedling injury. The amount used should be very limited and depends on the fertilizer formulation and soil properties. Possible advantages of pop-up placement include: no need for separate fertilizer opener on the planter, lower rate of fertilizer used, reduced amount of P on high P soils, and less fertilizer handling (fewer planter fill-ups). However, pop-up fertilizer applications should be used with extreme caution due to the potential for crop injury. No more than 10 lbs/acre N + K2O should be applied. Pop-up placement can be a good option if the proper rate and materials rules are followed and equipment can be adequately set for pop-up placement.  Do not apply diammonium phosphate (DAP – 18-46-0) or urea (46-0-0) due to the risk of seedling injury.

Yield response to starter fertilizer use.

Research has shown great variance in the ability of starter fertilizer to result in grain yield increases. Studies have shown that situations most likely to experience yield response from the use of starter fertilizer include: areas in the Northern Corn Belt and the Central Corn Belt that used reduced tillage, have poor drainage or soils with low P.

 

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Sources:

Beegle, D.B., Roth, G.W., and Lingenfelter, D.D. 2003. Starter fertilizer. Penn State University. Agronomy Facts 51. http://extension.psu.edu/ Hergert, G.W., Wortmann, C.S., Ferguson, R.B., Shapiro, C.A., and Shaver, T.M. 2012. Using starter fertilizer for corn, grain sorghum, and soybeans. University of Nebraska–Lincoln. NebGuide. G361. Hoeft, R. 2000. Will starter fertilizer increase corn yield? University of Illinois Extension. The Bulletin. http://bulletin.ipm.illinois.edu/ Nielsen, R. 2013. Root development in young corn. Purdue University Department of Agronomy. https://www.agry.purdue.edu/

Web sources verified 01/13/16. 140224070105

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